Leakage developer recirculation assembly

ABSTRACT

A tray is positioned beneath the developing station of an electro-statographic reproducing apparatus to catch developer which leaks from the developing station. The developer caught in the tray is transported therefrom and returned to the developing station.

United States Patent Lux May 20, 1975 {54] LEAKAGE DEVELOPER RECIRCULATION 3,639,050 2/1972 Staller.............................. 355/3 DD ASSEMBLY 3,65l,782 3/1972 MacDonald 355/") X 3,678,896 7/1972 Hewitt 8/637 [75] Inventor: Adalbert A. Lux, Penfleld, NY. 3,632,538 8/1972 Cade.. [73] Assignee: Xerox Corporalion,Stamford,Cnn. 3.637308 8"972 Mill" [22] Filed: May 1972 Primary Examiner-John M. Horan [2]] Appl. No.: 250,637 Attorney, Agent, or Firm-James J. Ralabate [52 US. Cl. 355/3 AB TRACT [51] [121. CI 603g /08 A tray is positioned beneath the developing station of [58} Field of Search 355/3, 4, 10, ll, l2, [5; an electrmstamgmphic reproducing apparatus to 8/637 catch developer which leaks from the developing station. The developer caught in the tray is transported Reiermces cued therefrom and returned to the developing station.

UNITED STATES PATENTS 878,003 9/1970 Altman 355/3 DD 7 Claims 3 Drawing Figures 3,543,720 12/1970 Drexler 355/3 DD X PATENTEB HAY 2 0 I975 SHEET 2 OF 3 FATE NIH] HAY 2 (H5175 SHEET 3 BF 3 LEAKAGE DEVELOPER RECIRC ULATION ASSEMBLY BACKGROUND OF THE INVENTION to dissipate the charge on the areas of the layer exposed to the light and developing the resulting latent electrostatic image by depositing on the image a finely divided electroscopic material referred to in the art as "toner." The toner is normally attracted to those areas of the layer which retain a charge. thereby forming a toner image corresponding to the latent electrostatic image. which may then be transferred to a support surface. such as paper. The transferred image is generally permanently affixed to the support surface by heating. although other suitable fixing means. such as solvent or overcoating treatment. may be substituted for the heat fixing step.

Many methods are known for applying the electroseopic particles to the latent electrostatic image to be developed. On development method as disclosed by E. N. Wise in U.S. Pat. No. 2.013.552 is known as cascade" development. In this method. developer material comprising relatively large carrier particles having finely divided toner particles electrostatically clinging to the surface of the carrier particles is conveyed to and rolled or cascaded across the electrostatic latent imagebearing surface. The composition of the toner particles is so chosen as to have a triboelectric polarity opposite that of the carrier particles. In order to develop a negatively chargcd latent electrostatic image. electroscopic powder and carrier combination should be selected in which the powder is triboelectrically positive in relation to the carrier. Conversely. to develop a positively charged latent electrostatic image. the elcctroscopic powder and carrier should be selected in which the powder is triboelectrically negative in relation to the carrier. This triboelectric relationship between the powder and carrier depends on their relative positions in a triboelectric series which the materials are arranged in such a way that each material is charged with a positive electrical charge when contacted with any material below it in the series and with a negative electrical charge when contacted with any material above in the series. As the mixture cascades or rolls across the image-bearing surface. the toner particles are electrostatically deposited and secured to the charged portions of the latent image and are not deposited on the uncharged or background portions of the image. Most of toner particles accidentally deposited in the background are removed by the rolling carrier. due apparently. to the greater electrostatic attraction between the toner and the carrier than between the toner and the discharged background. The carrier particles and unused toner particles are then recycled. This technique is extremely good for the development of line copy images. The cascade development process is the most widely used commercial electrophotographic development technique.

In a cascade developing system. there is some leakage of developer from the developing station between the moving electrostatographic recording surface and the developer catching lip of the developing station. In prior art machines. in some cases. a tray is positioned immediately below the developing station to catch developer which falls between the developer catching lip of the developing station and the electrostatographic recording surface. Although the use of such a catch tray is effective for preventing leaking developer from entering other parts ofthe machine. the build-up of developer in the tray causes some difficulties. Thus. for example. in machines where developer leakage may increase. the tray is inadequate for holding such increased quantities of developer. In addition. developer falling into the tray in which large amounts of developer are stored may result in toner clouds which derogatcs from the desired cleanliness of the machine.

SUMMARY OF THE INVENTION The principle object of the present invention is to provide an electrostatographic development system which alleviates the aforementioned difficulties.

The object of the present invention is broadly accomplished. in one aspect. by providing catch means for catching developer which leaks from the development station and transport means for transporting the developer from the catch means to a storage zone whereby developer is continuously removed from the catch means and build-up of developer in the catch means is prevented.

The storage means for the developer which leaks from the development station and is caught by the catch means may be either a separate storage unit or the developer sump of the development station. preferably the developer sump of the developing station. In the case where the developing station developer sump also functions as the storage means for the developer which has leaked from the developing station. there is essentially no loss of developer by leakage in that leaked developer is continuously recycled to the developing station.

In accordance with a preferred embodiment of the present invention the catch means for catching leaked developer includes a self-cleaning conveying means for conveying developer retained in the catch means to an exit port for ultimate transport to the storage zone. The self-cleaning conveying means is preferably in the form of an endless flexible member which revolves about two longitudinally spaced pulleys in the catch means. whereby stretching of the flexible member. upon moving around the pulleys. results in release of any developer which has been retained by the flexible member.

The present invention will be described in more detail with respect to a preferred embodiment thereof illustrated in the accompanying drawings.

THE DRAWINGS FIG. I is a simplified schematic representation of an electrophotographic reproducing machine incorporating an embodiment of the present invention;

FIG. 2 is a front elevational view, partly in section. of an embodiment of the developer leakage recirculation unit of the present invention; and

FIG. 3 is an isometric view of the embodiment illustrated in FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENT Referring now to the drawings. there is shown schematically in Fl(i. I an embodiment of the subject invention in a suitable environment such as an electrophotographic reproducing machine adapted for continuous and automatic operation, The machine includes an electrophotographic plate or surface It) formed in the shape of a drum. The plate has a photoconductbc or light responsive layer on a condt|cti\e backing. jour naled in a frame to rotate in the direction indicated by the arrow. The rotation will cause the plate to sequentially pass a series of electrophotographic processing stations. For the purpose of the present disclosure. the several electrophotographie processing stations in the path of movement of the plate surface may be described functionally as follows:

A charging station 20 at which a uniform electrostatic charge is deposited on the photoconductive plate;

An exposure station 30 at which a light or radiation pattern of the copy to be reproduced is projected onto the plate surface to dissipate the charge in the exposed areas thereof to thereby form a latent electrostatic image of the copy to be reproduced;

A developing station 40. including the recirculation unit of the present invention. at which clectrophotographic developing material. including toner particles having an electrostatic charge opposite that of the latent electrostatic image is cascaded over the plate surface whereby the toner particles adhere to the latent electrostatic image to fornt a visible toner image in an configuration of the copy being reproduced:

A transfer station 50. at which the toner image is electrostatieally transferred from the plate surface to a transfer ntaterial or a support surface and A drum-cleaning station 60 at which the plate surface is brushed to remove residual toner particles remaining thereon after image transfer and exposed to a relatively bright light source to effect substantially complete discharge of any residual electrostatic charge remaining thereonv It is felt that the preceding description ofthe electrophotographic process is sufficient for an understanding of the instant invention. Further details of this type of xerographic apparatus may be had by reference to US. Pat. No. 3.3t)l.l2o issued to R. F. Osborne et al.

The leakage developer recirculation unit 101 of the present invention includes a leakage developer catch assembly 102 and a leakage developer return conveyor assembly 130.

Referring to FIGS. 2 and 3 ofthe drawings. the catch assembly 102 is in the form of a tray H which extends axially along the length of the drum immediately below the space between the developing station 40 and the electrostatographic recording surface of the drum l0. The tray H0 is comprised of a bottom wall 11]. side wall 112. front wall H3 and rear wall 114. The side wall [12 is provided with an outlet means in the form of an exit port [15 positioned at the front end of the tray 110. The bottom wall 111 opposite side wall.

112 includes an upwardly angularly extending longitu dinal lip 116 positioned closely adjacent to the surface of the drum 10. with the lip 116 aiding in catching developer which has leaked from the developing station 40.

The tray lit) is protided with a conveying means in the form of an endless flexible member 121. such as the spring particularly shown. supported around longitudinally spaced drner pulley I22 and idler pulley 123 journaled to the bottom wall [ll of the tray H0. The driver pulley 12.! is drivingly connected to a drive means. in the form of motor 124. mounted on a support plate I25 which is mounted to the bottom wall 11] of tray 110.

The tray is positioned at an angle with respect to horizontal whereby developer retained in the tray 110 is urged toward the side wall 112. The tray is removably supported in such a position in a bracket [25. defining a track. which is mounted (not shown) to the frame of the developer housing of the development station 40. The forward portion of the tray [10 is not positioned in the bracket 126. whereby developer may freely flow front the tray through the exit port H5.

A conveyor assembly for returning leaked developer to the developer housing developing station 40 includes a conveyor comprised of an endless belt 13] carrying a plurality of buckets I32 movably mounted in a conveyor housing 133. The belt 13] is mounted about an idler roller [34 and a driven roller which is drivingly connected to a suitable drive means. such as motor 136. through a drive belt assembly 137 for driving the conveyor in the direction indicated by the arrow. The conveyor housing I33 includes an angularly outwardly upwardly extending lip 138 which is positioned adjacent to and immediately below the outlet port [[5 in tray ill). with the lip I38 functioning as a ramp or chute for transporting developer withdrawn through the port [[5 to a sump 139 formed in the bottom of the conveyor housing [33.

The top portion of the housing U3 is provided with a collection means for collecting and transporting developer dumped front the buckets I32 to the developer housing of development station 40. The collection means includes a shoulder portion 1-H having an angular bore 142 therein which is positioned to receive developer dumped from the buckets 132. A tube 143 is connected between the outlet of bore 142 and an inlet port in the developer housing of the development station 40 for transporting developer from the bore 142 to the developer housing of the development station 40.

In operation. developer which leaks between the drum l0 and the housing ofthe development station 40 is caught by tray lit). The developer caught in tray 110 is continuously transported by the flexible member 121 to the exit port US. As a result of the angular position of the tray 110. the developer falls through the exit port 115 onto the lip 138 of the conveyor housing 133, and from the lip 138 the developer falls into the sump 139. The developer is transported from the sump 139 by the buckets X32 and is dumped from the buckets 132, at the roller 135, into the bore [42 in shoulder 14]. The developer falls through bore 141 into return tube 143 and is transported through return tube 143 into the developer housing of the development station 40.

The conveying means defined by the spring 121, in tray H0, is self cleaning in that any developer entrapped in the spring is released therefrom by the expansion ofthe spring 121 around pulleys 122 and 123. ln this manner the tray H0 and the conveying means defined by spring 121 is maintained. at all times, essentially free of developer.

It is to be understood that the hereinabove described embodiment is merely illustrative of the present invention and. accordingly. numerous modifications thereof are possible within the spirit and scope of the invention. Thus. for example. instead of recirculating the developer to the developer housing. developer could be stored in a separate sump or storage zone. In such a modification. the conveyor assembly 130 could be eliminated. Similarly. the conveyor in the tray H0 could be other than a flexible member. as shown. although such a flexible member is preferred.

It is also to be understood that although the present invention has been particularly described with respect to an elcctrophotographic reproducing machine using a rotating drum as a recording surface. the present invention may also be employed in machines employing other types of recording surfaces: eg. a rotating belt. Similarly. although the present invention is particularly applicable to a machine using a cascade development technique. the present invention is also suitable for a machine using another development technique in which developer leakage is a problem.

It is further to be understood that the present invention is also applicable to electrostatographic processes other than the electrophotographic type. such as for example. electrostatic processes in which an electrostatic latent image is formed by a pulsing electrode.

The above modifications and others should be apparent to those skilled in the art from the teachings herein.

The present invention is particularly advantageous in that the developer which leaks from the development station is effectively and facilely recovered. In particular. there is no build-up of leaked developer which results in a cleaner operation. Furthermore. developer which would normly be lost from the system is effectively returned to the system. These and other advantages should be apparent to those skilled in the art from the teachings herein.

Numerous modifications and variations of the present invention are possible in light of the above teachings and. therefore. within the scope of the appended claims the invention may be practised other than as particularly described.

l claim:

l. in an electrostatographic apparatus containing a development station for developing an electrostatic la tent image formed on a surface including a developer housing in which solid developer is stored. transported to the electrostatic latent image bearing surface and received from said electrostatic latent image bearing surface. the improvement comprising:

catch means positioned externally to said developer housing for receiving solid developer which leaks past the developer housing during the development of the electrostatic latent image. said catch means comprising a tray positioned beneath said developer housing adjacent to the electrostatic latent image bearing surface to receive developer leaks between the electrostatic latent image bearing surface and the developer housing. said tray including an outlet port for withdrawing developer therefrom. and a conveying means in said tray for conveying developer within said tray to said outlet port. said conveying means comprising a movable endless belt journaled in said tray, and

means for transporting the developer from said outlet port to said developer housing.

2. The apparatus of claim I wherein said movable endless belt is comprised of a flexible member.

3. In an electrographic apparatus containing a cas' cadc development station for developing an electrostaie latent image formed on a surface including a developer housing in which solid developer is stored. transported to the electrostatic latent image bearing surface and received from said electrostatic latent image hearing surface. the improvement comprising:

catch means positioned externally to said developer housing for receiving solid developer which leaks past the developer housing during the development of the electrostatic latent image. said catch means comprising a tray positioned beneath said devel oper housing adjacent to the electrostatic latent image bearing surface to receive developer which leaks between the electrostatic latent image hearing surface and the developer housing. said tray including an outlet port for withdrawing developer therefrom. and a conveying means in said tray for conveying developer within said tray to said outlet port. and

means for transporting the developer withdrawn from said outlet port to said developer housing.

4. in an electrographic apparatus containing a development station for developing an electrostatic latent image formed on a surface including a developer housing in which solid de\eloper is stored. transported to the electrostatic latent image bearing surface and received from said electrostatic latent image bearing surface. the improvement comprising:

catch means positioned externally to said developer housing for receiving solid developer which leaks past the developer housing during the development of the electrostatic latent image. said catch means comprising a tray positioned beneath said developer housing adjacent to the electrostatic latent image bearing surface to receive developer which leaks between the electrostatic latent image hearing surface and the developer housing. said tray including an outlet port for withdrawing developer therefrom. and a conveying means in said tray for conveying developer within said tray to said outlet port. said conveying means comprising two spaced pulleys journaled in said tray and an endless flexible member supported in said tray around said two pulleys. and

means for transporting the developer withdrawn from said outlet port to said developer housing.

5. The apparatus of claim 4 wherein said endless flexible member is a spring.

6. In an electrographic apparatus containing a cascade development station for developing an electrostatic latent image formed on a surface including a developer housing in which solid developer is stored. transported to the electrostatic latent image bearing surface and received from said electrostatic latent image bearing surface. the improvement comprising:

catch means positioned externally to said developer housing for receiving solid developer which leaks past the developer housing during the development of the electrostatic latent image. said catch means comprising a tray. including a developer outlet aperture. said tray positioned below said cascade development station. said tray including a conveying means comprising first and second longitudinally spaced pulleys journaled in said tray. an endless flexible member mounted around said pulleys and drive means for driving one of said pulleys. said flexible member conveying developer in said tray to said developer outlet aperture. and

means for transporting the developer from said catch means to a developer storage zone. said transport means comprising a conveyor housing including a ramp for receiving developer from said outlet aperture and transporting said developer into said conveyor housing. a bucket conveyor journaled in said conveyor housing. means for conveying developer from said conveyor housing to said developer and means for driving said bucket conveyor to convey developer introduced into said conveyor housing to said means for conveying developer from said conveyor housing to said developer housing.

7. In an electrostatographic apparatus containing a development station for developing an electrostatic latent image formed on a surface including a developer housing in which solid developer is stored. transported to the electrostatic latent image bearing surface and received from said electrostatic latent image bearing sur face. the improvement comprising:

(all

catch means positioned externally to said developer housing for receiving developer which leaks past the developer housing during the development of the electrostatic latent image. said catch means comprising a tray positioned beneath said developer housing adjacent to the electrostatic latent image bearing surface to receive developer which leaks between the electrostatic latent image bearing surface and the developer housing. said tray including an outlet port for withdrawing developer therefrom. and a conveying means in said tray for conveying developer within said tray to said outlet port. said tray further including a lip portion and a vvall member opposite said lip portion of said tray. said lip portion being positioned adjacent said electrostatic latent image bearing surface. said wall member including said outlet port. said tray being supported at an angle with respect to horizontal to image developer toward said \vall member. and

means for transporting the developer withdrawn from said outlet port to said developer housing. 

1. In an electrostatographic apparatus containing a development station for developing an electrostatic latent image formed on a surface including a developer housing in which solid developer is stored, transported to the electrostatic latent image bearing surface and received from said electrostatic latent image bearing surface, the improvement comprising: catch means positioned externally to said developer housing for receiving solid developer which leaks past the developer housing during the development of the electrostatic latent image, said catch means comprising a tray positioned beneath said developer housing adjacent to the electrostatic latent image bearing surface to receive developer leaks between the electrostatic latent image bearing surface and the developer housing, said tray including an outlet port for withdrawing developer therefrom, and a conveying means in said tray for conveying developer within said tray to said outlet port, said conveying means comprising a movable endless belt journaled in said tray, and means for transporting the developer from said outlet port to said developer housing.
 2. The apparatus of claim 1 wherein said movable endless belt is comprised of a flexible member.
 3. In an electrographic apparatus containing a cascade development station for developing an electrostaic latent image formed on a surface including a developer housing in which solid developer is stored, transported to the electrostatic latent image bearing surface and received from said electrostatic latent image bearing surface, the improvement comprising: catch means positioned externally to said developer housing for receiving solid developer which leaks past the developer housing during the development of the electrostatic latent image, said catch means comprising a tray positioned beneath said developer housing adjacent to the electrostatic latent image bearing surface to receive developer which leaks between the electrostatic latent image bearing surface and the developer housing, said tray including an outlet port for withdrawing developer therefrom, and a conveying means in said tray for conveying developer within said tray to said outlet port, and means for transporting the developer withdrawn from said outlet port to said developer housing.
 4. In an electrographic apparatus containing a development station for developing an electrostatic latent image formed on a surface including a developer housing in which solid developer is stored, transported to the electrostatic latent image bearing surface and received from said electrostatic latent image bearing surface, the improvement comprising: catch means positioned externally to said developer housing for receiving solid developer which leaks past the developer housing during the development of the electrostatic latent image, said catch means comprising a tray positioned beneath said developer housing adjacent to the electrostatic latent image bearing surface to receive developer which leaks between the electrostatic latent image bearing surface and the developer housing, said tray including an outlet port for withdrawing developer therefrom, and a conveying means in said tray for conveying developer within said tray to said outlet port, said conveying means comprising two spaced pulleys journaled in said tray and an endless flexible member supported in said tray around said two pulleys, and means for transporting the developer withdrawn from said outlet port to said developer housing.
 5. The apparatus of claim 4 wherein said endless flexible member is a spring.
 6. In an electrographic apparatus containing a cascade development station For developing an electrostatic latent image formed on a surface including a developer housing in which solid developer is stored, transported to the electrostatic latent image bearing surface and received from said electrostatic latent image bearing surface, the improvement comprising: catch means positioned externally to said developer housing for receiving solid developer which leaks past the developer housing during the development of the electrostatic latent image, said catch means comprising a tray, including a developer outlet aperture, said tray positioned below said cascade development station, said tray including a conveying means comprising first and second longitudinally spaced pulleys journaled in said tray, an endless flexible member mounted around said pulleys and drive means for driving one of said pulleys, said flexible member conveying developer in said tray to said developer outlet aperture, and means for transporting the developer from said catch means to a developer storage zone, said transport means comprising a conveyor housing including a ramp for receiving developer from said outlet aperture and transporting said developer into said conveyor housing, a bucket conveyor journaled in said conveyor housing, means for conveying developer from said conveyor housing to said developer and means for driving said bucket conveyor to convey developer introduced into said conveyor housing to said means for conveying developer from said conveyor housing to said developer housing.
 7. In an electrostatographic apparatus containing a development station for developing an electrostatic latent image formed on a surface including a developer housing in which solid developer is stored, transported to the electrostatic latent image bearing surface and received from said electrostatic latent image bearing surface, the improvement comprising: catch means positioned externally to said developer housing for receiving developer which leaks past the developer housing during the development of the electrostatic latent image, said catch means comprising a tray positioned beneath said developer housing adjacent to the electrostatic latent image bearing surface to receive developer which leaks between the electrostatic latent image bearing surface and the developer housing, said tray including an outlet port for withdrawing developer therefrom, and a conveying means in said tray for conveying developer within said tray to said outlet port, said tray further including a lip portion and a wall member opposite said lip portion of said tray, said lip portion being positioned adjacent said electrostatic latent image bearing surface, said wall member including said outlet port, said tray being supported at an angle with respect to horizontal to image developer toward said wall member, and means for transporting the developer withdrawn from said outlet port to said developer housing. 